STM32F411CEU6 - RTC HW implementation

[MartinL]

Hello, 

I want to ask what is necessary for implementation of 32.768khz RTC XTAL to STM32F411CEU6?

In AN3060 I saw in chapter 3, fig6 that external load caps are not needed because they are implemented in STM32 MCU. Then I checked STM32F411CEU6 datasheet and there is figure25 where is example that resonator have these caps in the package.

What is correct? Provided information in ST documents quite confused me.

I have this XTAL - ABS06-32.768KHZ-1-T

Thank you for your advide. 

Regards, 

Martin

[Tesla DeLorean]

Isn't that APP NOTE for a COMPLETELY different series of stand-alone RTC?

https://www.st.com/resource/en/application_note/an3060-applications-guide-for-serial-realtime-clocks-rtcs-stmicroelectronics.pdf

Pretty sure you want a 6-7pF 32.768 KHz crystal with load capacitors on the STM32F4

AN2867 is for the STM32's

https://www.st.com/resource/en/application_note/an2867-guidelines-for-oscillator-design-on-stm8afals-and-stm32-mcusmpus-stmicroelectronics.pdf

[Tesla DeLorean]

ABS06-32.768KHZ-1-T is a 12.5pF crystal, I'd not be using that for F1/F2/F4 devices.

ST has example designs in the form of DISCO and EVAL boards, go the the web pages for the products, under the "CAD Resources" tab you can find schematics and BoM

[Tesla DeLorean]

https://stm32-base.org/boards/STM32F411CEU6-WeAct-Black-Pill-V2.0.html

https://stm32-base.org/assets/pdf/boards/original-schematic-STM32F411CEU6_WeAct_Black_Pill_V2.0.pdf